mahoney944

So for the past few mornings when I go to start my car. The motor starts up normal but the voltage stays just a hair over the 12 mark and the low voltage red light stays on and oddly the anti lock brakes light stays on. I find that if I rev the motor to maybe 2000 the anti lock brake light goes off, the red low voltage light goes out and my volts raise to 14v ( Nissan alt mod) and its perfectly normal from then on. What I find stranger is it only seems to happen first thing in the morning, but not at all the rest of the day. It has been raining a lot the past 2 and a half weeks but I'm not sure if that has any effect on what's happening. I'm not killing my battery, and not having starting issues, it almost seems like the alternator is still sleeping when I first fire it up in the morning, and that light rev wakes it up. Not sure what could be the issue. If I don't rev it the lights stay on and voltage stays low. After the rev, its as normal as can be. Also what connection does the voltage have with the anti lock brake light? To make them in sync with coming on and going off together with the rev? Thoughts? And the Nissan alt mod was done long ago so the wiring is good, and to be clear after the rev the problem is non existing.

Alan 91 C2

I would check/replace the voltage regulator/brush set. The regulator is not making enough field current to kick the alternator into charge territory.

On the old generator cars, prior to alternators, the residual magnetic field in the generator would pull in the regulator. When the residual field strength was weak, they would act just like your situation.

mahoney944

I dont know much about alternator internals, is the voltage regulator / brush set one in the same or are they separate parts?

Humboldtgrin

Sound like your regulator went out. Rather not go into the details of how a regulator works. But you should have your alternator rebiult. The regulator is most likely bad and old and so are the brushes and bearings. I bet if you have you alternator repaired your voltage and ABS lights will go away.

mahoney944

They do go away though after a quick rev and continue to stay out / work properly after the rev. And the charge stays perfect. Why would it work fine after just one rev and continue to work perfectly even on start ups later that same day. I would think it would just work or not work if the regulator was shot. And the alt is less than a year old.

nofalls

Loose belt?

mahoney944

Not loose I actually thought to loosen it a hair. Because it seemed maybe a little tight but it nothing that would cause too much trouble. I just left work after it sat all day. Zero issues. It's almost like the early morning is effecting something somehow

mahoney944

If the regulator was bad, wouldn't it cause the issue consistently? It only seems to happen in the morning and its not every morning either. Of course the morning start is after the car sat all night long, giving the longest dwell from the last start. Where work starts are after a 8 hour shift. So its a shorter sit. Hmmm

Alan 91 C2

The regulator and brushes are in one piece, about $35.

mahoney944

http://m.ebay.com/itm/290444092207?_trksid=p3984.m1423.l2649&_mwBanner=1#ht_1705wt_924This is the exact alternator I did my Nissan alt mod with, your saying the regulator for this alternator has the brushes as a part of it? So I just need the regulator?

Willard Bridgham 3

Sounds like a temperature dependent transient. After the electrical system warms up, contacts expand.

mahoney944

Seems to be.

mahoney944

Time is definitely the key here, I let the car sit all yesterday from 4 pm until this morning around noon. I got my volt meter ready and started it up. (note the weather is nice and warm today.) The car's volts were low and stayed low, I checked the alternator and it read just over 12 volts and then I checked the battery, and got about the same, I cracked the throttle body over to give it a short rev and the alternator jumped to 14.4 volts, and read 14.3 at the battery. It's definitely the alternator acting up, so I guess I'll order some parts or maybe just a second spare alternator for how cheap they are.....

I was also wondering what the normal drop in voltage is from the alternator to the battery. Once my alternator kicked on, I saw 14.4 at the alternator and 14.3 at the battery. I assume this is probably normal but I just wanted to be sure. Should I be seeing the same voltage from the alternator to battery, or is the .1v difference normal, assuming the circuit uses some energy?

mahoney944

The new alternator came in, I extracted the internal voltage regulator which was fairly easy. Installed it in my alternator and so far it's worked flawlessly. I'll have to keep an eye on it over the next few days but it seemed to work. For anyone looking to do this on a Nissan alt, know the internal voltage regulator and brushes are inside the alternator and are one piece. It requires you to remove the rear casing, so it was a little more involved then changing a stock one. In total maybe an hour or two of work to remove my alternator, swap parts, and reinstall.

Alan 91 C2

good job.